WordPress 调用指定栏目（分类）下的所有标签

最近接了一个WordPress定制开发的项目，有一个需求就是在不同的栏目下显示不同的标签云，需要根据栏目（分类）ID，调用该栏目下的所有标签，包含该栏目子栏目的所有标签，实现方法如下：

首先在主题的functions.php文件中加入如下函数：

function get_category_tags($args) {
    global $wpdb;
    $tags = $wpdb->get_results
    ("
        SELECT DISTINCT terms2.term_id as tag_id, terms2.name as tag_name, null as tag_link
        FROM
            wp_posts as p1
            LEFT JOIN wp_term_relationships as r1 ON p1.ID = r1.object_ID
            LEFT JOIN wp_term_taxonomy as t1 ON r1.term_taxonomy_id = t1.term_taxonomy_id
            LEFT JOIN wp_terms as terms1 ON t1.term_id = terms1.term_id,

            wp_posts as p2
            LEFT JOIN wp_term_relationships as r2 ON p2.ID = r2.object_ID
            LEFT JOIN wp_term_taxonomy as t2 ON r2.term_taxonomy_id = t2.term_taxonomy_id
            LEFT JOIN wp_terms as terms2 ON t2.term_id = terms2.term_id
        WHERE
            t1.taxonomy = 'category' AND p1.post_status = 'publish' AND terms1.term_id IN (".$args['categories'].") AND
            t2.taxonomy = 'post_tag' AND p2.post_status = 'publish'
            AND p1.ID = p2.ID
        ORDER by tag_name
    ");
    $count = 0;
    foreach ($tags as $tag) {
        $tags[$count]->tag_link = get_tag_link($tag->tag_id);
        $count++;
    }
    return $tags;
}

在需要调用标签的模板文件对应位置处加入下面的代码，可以指定多个分类ID。

$args = array(
        'categories'                => '12,13,14'
    );

$tags = get_category_tags($args);

上面的代码会返回一个标签数组，循环输出即可，比如：

$content .= "<ul>";
foreach ($tags as $tag) {
    $content .= "<li><a href="$tag->tag_link">$tag->tag_name</a></li>";
}
$content .= "</ul>";
echo $content;